Pulsed ignition circuits are commonly used for starting many discharge lamps. This circuit can be an ignitor which provides sufficient energy in a voltage pulse which is applied to lamp electrodes to break down the gasses in the lamp arc tube allowing enough current to flow in order to start the lamp U.S. Pat. No. 4,695,771 describes a typical, prior art ignitor circuit which is useful with both autotransformer and choke-type magnetic ballast.
Most prior art ignitor circuits operate continuously, whenever power is applied to the lamp fixture, to apply at least one ignition pulse per half cycle of the AC line voltage until the lamp lights. Good lamps start virtually immediately; however, burned-out lamps will not start and the ignitor will thus pulse continuously. Some quarters of the lighting users and industry have expressed concern that stress imposed by a continuous train of ignition pulses could shorten the life of insulation and/or electronic components associated with the ballast and lighting fixture.
In addition, at their end-of-life, many high intensity discharge lamps go through an on and off cycling phase that may last several weeks. In this phase, the aged lamp turns itself off due to the arc voltage increase that has taken place over time. Since the power to the ballast is still on, the ignitor immediately starts pulsing. In a minute to several minutes, the lamp cools down enough to be restruck by the ignitor.
This cycling can be particularly annoying and/or disturbing to anyone who must be in the presence of such lamps. Also, by the time discharge lamps start their cycling phase, their performance characteristics such as lumen efficacy and/or color have deteriorated significantly. Allowing cycling lamps to remain active means that the user of those lamps is not benefiting from the lighting installation in the way it was intended. He will be experiencing distinctly lower light levels, and/or color distortion as he tries to perform his tasks under such lamps.
Lamp cycling can also be particularly disadvantageous in applications such as highway lighting since service crews which happen down the road during the period when the lamp is in the illuminated phase of the cycle will fail to detect the need to change a lamp.
U.S. Pat. No. 4,665,346 describes a lamp auxiliary circuit with a starter circuit which is controlled by a timer, so that it only operates for a predetermined period after power is applied to the circuit. This patent further describes logic circuits which are designed to prevent on-off cycling of high intensity discharge lamps as arc voltage increases at end-of-life.
In many discharge lamp installations, maintenance crews re-lamp fixtures while they are "hot"; that is lamps are replaced without first removing line voltage from the fixture. If a lamp ignitor circuit is controlled by a timer so that it will not operate except for a specified period after power is applied, the ignitor circuit will not immediately activate the new lamps after hot installation, in which case their operation cannot be verified by maintenance personnel.